302 THE CIRCULATION. 



slow, yet as the distance to be passed over between the arteries and 

 veins is very small, the blood really requires but a short time to 

 traverse the capillary system, and to commence its returning passage 

 by the veins. 



GENERAL CONSIDERATIONS. 



The rapidity with which the blood passes through the entire round 

 of the circulation is a point of great interest, and one which has 

 received a considerable share of attention. The results of such 

 experiments, as have been tried, show that this rapidity is much 

 greater than would have been anticipated. Hering, Poisseuille, and 

 Matteucci, 1 have all experimented on this subject in the following 

 manner. A solution of ferrocyanide of potassium was injected 

 into the right jugular vein of a horse, at the same time that a liga- 

 ture was placed upon the corresponding vein on the left side, and 

 an opening made in it above the ligature. The blood flowing from 

 the left jugular vein was then received in separate vessels, which 

 were changed every five seconds, and the contents afterward exa- 

 mined. It was thus found that the blood drawn from the first to 

 the twentieth second contained no traces of the ferrocyanide ; but 

 that which escaped from the vein at the end of from twenty to 

 twenty-five seconds, showed unmistakable evidence of the presence 

 of the foreign salt. The ferrocyanide of potassium must, therefore, 

 during this time, have passed from the point of injection to the 

 right side of the heart, thence to the lungs and through the pulmo- 

 nary circulation, returned to the heart, passed out again through 

 the arteries to the capillary system of the head and neck, and 

 thence have commenced its returning passage to the right side of 

 the heart, through the jugular vein. 



By extending these investigations to different animals, it was 

 found that the duration of the circulatory movement varied, to 

 some extent, with the size and species. In the larger quadrupeds, 

 as a general rule, it was longer ; in the smaller, the time required 

 was less. 



In the Horse, 2 the mean duration was 28 seconds. 

 " Dog " " " " 15 " 



" Goat " " " " 13 " 



w. F OX c< u t< 12$ " 



Rabbit " " " " 7 " 



1 Physical Phenomena of Living Beings, Pereira's translation, Philada. ed., 1848, 

 p. 317. 



2 In Milne Edwards, Logons sur la Physiologie, &c., vol. iv. p. 364. 



